In the art of vibrating type angular rate sensors it is known that a vibrating element subjected to an angular turn rate about certain axes will experience resultant forces and/or deflections which are an indication of the magnitude of the input turn rate.
Several problems associated with the implementation of this effect have kept this type of instrument from seeing as widespresd use as the spinning rotor type rate sensor despite its advantages of simplicity, elimination of bearings, cost, and longer life.
One problem associated with attaining accurate measurements from a vibrating element angular rate sensor is that of accurately measuring or controlling the amplitude of vibration. Lyman, in U.S. Pat. No. Re. 22,409, teaches that the combination of forced vibration action with an applied input turn rate causes resultant forces which deflect the vibration pattern to an elliptical path. With the length of the major axis of the ellipse held constant, the width of the minor axis of the ellipse is a function of the input rate of turn. Since the resultant forces/deflections are directly related to vibration amplitude as well as the input turn rate, amplitude must be at least as accurately controlled or "measured" as the stated accuracy of the complete system, typically within 0.01% or better.
It is one object of this invention to disclose a means by which resultant signals are generated that are directly related to input turn rate and essentially independent of vibration amplitude. This reduces the importance of amplitude control several orders of magnitude to that required by other design parameters such as stress levels, vibrational clearances, etc. Typically, 10% accuracy is then adequate for these other design parameters.
Another problem associated with vibrating element angular rate sensors has been creating a vibrating element that can be fixedly attached to a frame "for mounting purposes" without motion or forces in the attachment or the frame interfering with the accuracy of the resultant measured signals. Traditionally, the primary method of attaining resultant signals from a vibrating element has been to simply fixedly attach the element to a "rigid frame" and measure the resultant forces/deflections with respect to the frame either directly or with implied respect depending on the type of pickoffs used. Since the resultant forces are transmitted directly to the frame, error signals can be generated due to motion of the frame caused by these applied forces or from external sources.
.Iadd.These error signals are due to the fact that the vibrating elements are not balanced for both the driven and reaction directions of vibration. A balanced structure precludes forces from entering or leaving the system comprising the vibrating elements and thereby isolates the vibrating elements from outside vibration and interference. .Iaddend.
Examples of geometrics of this nature would be the traditional tuning fork type (ref. Lyman U.S. Pat. No. Re. 22,409), the cantilever beam type (ref Jacobson U.S. Pat. No. 4,267,731), the vibrating wire type (ref Johnson U.S. Pat. No. 3,903,747), etc. A previous method of dealing with the resultant forces without transferring them directly to the frame has been to attach a second and similar vibrating system to the first vibrating system whereby forces/deflections from either the forced vibration action or as a resultant from an input turn rate from one system are counter opposed by the other, resulting in a "node" to which the frame attachment is made.
This method unnecessarily doubles the complexity of the unit thereby increasing cost and unreliability. Also, the "node" defined by this method is typically a thin plane to which only a tenuous attachment can be made resulting in sensitivities in low levels of vibration and accelerations about the attachment.
It is a second object of this invention to disclose a means of creating a vibrating element angular rate sensor that can be rigidly attached to a frame "for mounting purposes" without motion or forces in the attachment or the frame causing errors in the resultant measurement signals.